Mechanically governed diesel engines have long been used in hazardous and other sensitive environments. Hazardous environments include environments that have flammable or explosive vapors or dust such as those found in oil fields or in coal mines. The presence of these vapors and dust pose a possibility of a runaway condition of the engine due to ingestion of these ambient combustible vapors and dust through the air intake of the engine and subsequent combustion in the cylinders. Other sensitive environments may include use at or near heavily populated and enclosed sites such as in large or tall buildings with engines driving a water pump or generator.
For use in these hazardous or sensitive sites, various aftermarket components are installed on the engine to provide an engine shut down if there is an indication that the engine is not working properly, for example, it is in a runaway condition. For engine shut down in the event of a runaway condition, a shut down system may include closure of an intake air flap or actuation of a halon injection system as well as a fuel shut off system that is activated when the engine achieves or exceeds a trigger point; i.e., an actuation set point at a certain speed.
For many automatic shut down devices, various government or other certification agencies require periodic testing to determine if the shut down systems are properly working and properly maintained. For runaway speed shut down systems, these tests are often conducted at runaway speeds, for example, tested at 2400 rpm on a 2100 rpm rated engine. These runaway speed conditions are easily achieved on a mechanically governed engine by adjustment of the fuel rack to cause a runaway condition that reaches the trigger point. Once the overspeed runaway condition is met, it can be determined if the automatic shut down system operated according to expectation and specifications.
One of the great improvements to the diesel engine in recent times is the incorporation of electronic controls. These electronically controlled diesel engines, also referred to as electronically governed diesel engines, most commonly incorporate an electronic control module (ECM). The ECM is loaded with a set of running calibrations, most commonly referred to as a primary or main rating along with a droop component commencing at the full load speed when the horsepower output drops to zero at higher speeds. Electronic control modules provide many advantages over mechanically governed diesel engines, including more precise control of fuel, emission vapors, and various other engine functions and provide for better reliability and less maintenance of the control settings. In summary, electronically controlled diesel engines provide a more reliable, cleaner and more fuel efficient engine. As a consequence of the many advantages provided by electronic controls, the electronically controlled diesel engine has seen a great rise in popularity.
However, there are still many markets and applications that have not opened to these otherwise advantageous electronically controlled diesel engines. Electronically controlled diesel engines have not yet been allowed to be used in building basements for use as a water pump for fire control. In addition, oil fields and coal mines are still dominated by mechanically governed diesel engines.
The reasons for the lack of entry of the electronically controlled diesel engine in these particular marketplaces in spite of its obvious advantages in fuel economy, superior emission control and performance is due to a single cause; namely, there is no available test to determine the operability of the shut down system during overspeed. Once the calibrations have been set in the electronic control module, the controls to date have not provided for an overspeed testing of the shut down system or, for that matter, any type of testing of any shut down system that may be connected to the engine.
What is needed is a testing method for an electronically governed engine for determining the operability of an overspeed and other automatic shut down systems. What is also needed is a testing method for an electronically governed engine for determining the operability of an overspeed shut down system for the engine during actual overspeed conditions. What is also needed is a testing method that allows testing calibrations to be entered into the electronic control module to provide an output signal from the electronic control unit to actuate the overspeed shut down system.